Such a welding head such as that known from DE 10 2004 060 389 Al may serve for welding metallic components that are not rotationally symmetrical (for example holders, earth flanges or the like) onto metallic workpieces, such as for example body sheets of motor vehicles. The component generally has in this case a welding surface which is much longer in one direction than in the direction transverse thereto.
The basic technology for this type of welding process corresponds to what is known as stud welding. The welding-on operation is consequently performed with preference by the rapid drawn-arc method with magnetic arc deflection.
Devices for drawn-arc welding by means of magnetic arc deflection have long been known and have proven successful in practice. For example, U.S. Pat. No. 2,406,474 from 1946 already shows a device or stud welding and a circuit for stabilizing a welding arc. For this purpose, the invention uses a coil with a winding which is connected in series to the conductor of the welding current. This has the consequence that a magnetic field is formed at the same time as the welding current flows. The stud holder, which is located in the centre of the coil, serves as a coil core.
In U.S. Pat. No. 2,413,189 shows a device for welding studs which is intended for manual use. The document also shows that it is necessary to make the supply lead for the welding current flexible, since it is necessary according to the method to move the stud holder away from the workpiece in a lifting movement.
DE 1 565 003 likewise shows a device for welding fastening elements by arc stud welding on the drawn-arc principle. In this device too, a coil comprising a winding is connected in series to the welding current and arranged around the welding location. The purpose of these devices is, on the one hand, to avoid a blasting effect of the arc and, on the other hand, to produce rotation of the arc when welding tubular components (fastening elements).
DE 102 53 415 discloses a method and a device for welding on rectangular sheet metal brackets. This device likewise has a coil arrangement, which is intended to produce a linear movement of the arc. By contrast with the documents mentioned further above, in this case the coil arrangement is not connected in series with the welding current.
The use of protective gas by means of directing it as a stream is disclosed in DE 196 38 287. Here, protective gas is directed onto the joining location from the side and makes oxide-free soldering possible, since the ambient air is blown away by the stream applied.
However, a disadvantage of the aforementioned methods and devices is that cables carrying welding current have to be laboriously led out from the device housing into the front welding region. The rigidity and, most particularly, the inert mass of these welding-current-carrying cables, which have to be relatively sturdy on account of the high current intensity, lead to hindrances in the sequences of movements. In the case of arc stud welding by the drawn-arc method, reciprocating movements take place in the range of milliseconds and therefore represent highly dynamic processes.